Spark plug



Patented June 6, 1944 2,350,415 SPARK PLUG Hector Rabezzana, Flint,Mich., assignor to General Motors Corporation, Detroit, Mich., acorporation of Delaware Application July 6, 1942, Serial No. 449,896

6 Claims.

My invention relates to spark plugs designed to ignite successivecharges of air and hydrocarbon supplied to and burned within the workingcylinder of an internal combustion engine; and particularly to sparkplugs adapted to be used with a conductor which supplies current to thecentral electrode of the plug and is enclosed in a metallic casingattached to the shell of the plug so as to be grounded to the enginethrough the shell; or used with a supply conductor which is not enclosedin a metallic casing secured to the shell in which case the supplyconductor is connected with the plug and supplies current to the centralelectrode, but has no grounded metallic casing enclosing the same. Thesupply conductor whether enclosed in a grounded metallic casing or notis separate and independent of the plug itself; and the conductor andplug being independent of each other and made as separate devices orparts it follow that while the two must be used together in an engineignition system, either may be replaced should it become necessary to doso without replacing the other. The spark plug unit comprises a hollowinsulating member made, preferably, of ceramic material housed in itsentirety within an outer metallic shell or casing threaded at its lowerend to screw into an internally threaded opening in an internalcombustion engine cylinder, and threaded at its upper end to facilitatethe attachment thereto of a supply conductor which extends into thehollow. insulating member aforesaid, and whereby current is supplied tothe central insulated electrode of the plug; and which supply conductormay or may not be enclosed within an outer metallic casing which lastnamed casing when used is secured to the casing of the plug, so as to begrounded to the engine.

The object of my invention, therefore, is to provide a spark plug andsupply conductor combination wherein current may be supplied to thecentral electrode of the plug by a supply conductor such as is disclosedin my Patent No. 2,238,397, April 15,1941, the same either having or nothaving an outer grounded metallic shield for enclosing the conductorwhereby current is supplied to the central electrode of the plug; andwherein the plug part of the combination has features of constructionand operation such as are hereinafter particularly referred to.

Referring now to the drawing accompanying and forming a part of thisspecification and wherein the preferred form of my invention isillustrated:

Figure l is a view showing a section upon a central plane of the sparkplug part of my invention, the conductor whereby currentis supplied tothe insulated electrode thereof being omitted because it issubstantially the same as the one disclosed in my patent above referredto.

Figure 2 is a perspective view showing an annular dished member forspacing the upper end of the insulating member shown in Figure 1concentrically Within the hollow shell of the plug.

Figure 3 is a view showing a cross-section of another form of annularholding member used as a part of my improved spark plug.

Figure 4 is a fragmentary view showing my invention modified as tocertain of the features thereof.

Referring now to the drawing, the numeral 5 des gnates an integralhollow shell or casing cylindrical in form and threaded at its lowerend, as indicated by the numeral 6, so as to screw into a threadedopening in an internal combustion engine cylinder; and threaded at upperend I to permit the attachment thereto of a supply conductor which, asexplained, may or may not be enclosed within a metallic shield tube. Ifthus enclosed as in my patent hereinbefore referred to the shield whichcontains the supply conductor is secured to the shell as by a suitablegland nut and is thus grounded to the engine the shell 5 being of metal)through the shell or casing of the plug, and the plug becomes one of theso-called radio shielded class; whereas if not provided with a metallicshield the supply conductor is secured to the shell by a suitable glandnut engaging the thread I, and a packing (which need not be conductive)engaging the usual rubber or equivalent insulation of the supplyconductor.

The shell or casing 5 contains an insulating member 8 which has a largeinternal chamber 9 which extends from the upper end of the plug downwardinto the insulating member, and a passage of lesser d ameter extendingfrom the chamber 9 downward and through the lower end'of the insulatingmember and through which the insulated electrode I0 of the plug extends:this neither of its ends projects beyond the ends of the casing 5; andwhen the plug is in use the supply conductor (not shown) extends intothe internal chamber 9 and makes electrical contact with the upper endof the insulated electrode III, which conductor is secured to the shellor casing of the plug as by a gland nut in threaded engagement with thethreaded upper end I of the shell 5 as hereinbefore explained.

The lower portion of the insulating member 8 has an outer annular seatl2 which cooperates with a similar seat l3 within the casing to supportsaid member, a suitable gasket M being used to secure gas-tightnessbetween the parts; and the' insulating member is held in place withinthe shell by flange l5 integral with the shell; and which flange isturned inward as shown and into engagement with the upper end of aC-shaped (in cross section) metallic member l6, which cooperates with anexternal annular shoulder I I of my invention may be of crescent form incrosssection, as illustrated in Fig. 3, or the wall thereof may.approach a more uniform thickness as in Fig. 1. The upper end of theinsulating member 8|, however, has a flat annular shoulder Ill-insteadof an inclined shoulder as in Fig. 1' which supports an annular washerIN; the periphery of which, however, does not extend to and engage theinner wall of the casing of the plug as in the form illustrated in Fig.l. The C-shaped metallic member l6l in this form of my invention is heldin place within and below the upper extremity of the shell to therebyretain the parts in assembled relation by an inturned holding flange l5!integral with the shell, the same as in the form of my inventionhereinbefore described.

-Having thus described.and explained my invention I claim and desire tosecure by Letters thereupon to hold the insulating member in place I byit is supported, during the intuming of they holding flange l5 intoengagement with the upper end of the holding member IS. The periphery IQof this spacing member is forced into engagement with thejinterior ofthe upper end of the casing during the assembling of the parts, asaforesaid, and acts to position the upper end of the insulating memberconcentrically within the shell or casing as will be understood.

The annular metallic holding member [6 is shown as of a form whichclosely approximates the'form of the equivalent holding member disclosedin my Patent No; 2,129,962, September 13, 1938. Figure 3, however,illustrates a holding member 20 which, because of its closerapproximation (in cross-section) to a crescent shape, results in asomewhat more uniform distribution of fiber'stress within and throughoutthe material of the holding member than is commonly present in the formof holding member disclosed. in my said patent. In this other form ofholding member (Figure 3) the upper and lower ends of said member(because theyare less stiff than the middle part thereof) yield morereadily than in the stiffer and more resistant form disclosed in' saidpatent, because of increased flexibility of a crescent form; and moreuniform tension stresses result in the outer part 2| of said member, andlikewise more uniform compression stresses in the inner zone 22 of saidmember; these characteristlcs inherent in a crescent form of holdingmember being manifest by more uniform deformation of said member thancommonly results in .the use of a holding member not crescentshaped incross-section, such as is present in my patent above noted.

Patent:

1. In a spark plug of the class described, a hollowmetallic shell orcasing having externally threaded portions at both its ends; an internalannular supporting ledge within said shell; an insulating member withinsaid shell and supported by said ledge and having an internal chamberwithin its upper portion, and an external annular shoulder adjacent itsupper end; an annular spacing disc supported upon said shoulder and theouter edge of which extends to and contacts with the interior of saidshell; an

low metallic shell or casing having externally threaded portions at bothits ends; an internal annular supporting ledge within said shell; aninsulating member within said shell and supported by said ledge andhaving an internal chamber within its upper portion. and an externalannular shoulder adjacent its upper end; 7 an annular spacing disc ofdished form supported upon said shoulder and the periphery of whichcontacts with the interior of said shell; an an nular holding memberc-shaped in cross-section within said shell and surrounding the upperextremity of said insulation member, and which In the modified form ofmy invention illus- I holding member rests upon the spacing discaforesaid; an inwardly extending flange integral with, and whichoverlays the upper end of said holding member to thereby hold saidseveral parts in. assembled relation with one another; and an insulatedelectrode extending from the lower end of the internal chamber aforesaiddownward 3. In a spark plug of the class described. a

hollow metallic shell or casing having an integral annular supportingledge adjacent its lower end;

an insulating member within saidshell and supported by said ledge andhaving an external annular shoulder adjacent its upper end; meanssupported upon said shoulder and contacting the shell for spacing theupper end of said insulating member concentrically within said shell; anannular holding member crescent-shaped in crosssection associated withsaid annular shoulder and surrounding the upper end of said insulatingmember; means at the upper end of said shell for holding said severalparts in assembled relation with one another;'and a central electrodewithin a passage provided for it in said insulating member.

4. In a spark plug of the class described, a hollow metallic shell oreasing having an internal annular supporting ledge adjacent its lowerend; an insulating member within said shell and supported by said ledgeand having an external annular shoulder adjacent its upper end; anannular holding member crescentshaped in cross-section associated withsaid annular shoulder and surrounding the upper end of said insulatingmember; an inwardly extending flange'integra-l with the upper end of sad casing and which flange overlays the upper end of said annular holdingmember and serves to hold the parts aforesaid in assembled relation withone another; and a central electrode within a passage provided for it insaid insulating member.

5. In a spark plug, a shell with an annular internal shoulder at adistance from its outer end, an electrode-carrying insulator which isreduced in diameter from a point at a distance from its inner enddisposed within the shell and seated on the annular internal shoulder onthe shell, an annular member which encircles the portion of theinsulator which is reduced in diameter and contacts the insulator andthe side wall of the shell to center the insulator in the shell, andannular means to hold the insulator in place in the shell seated on theannular member.

6. In a spark plug, a shell with an.annular internal shoulder at adistance from its outer end, an electrode-carrying insulator which isconcavely tapered to a smaller diameter from a point at a distance fromits inner end disposed within the shell and seated on the annularinternal shoulder on the shell, an annular member which is seated on thetaper at a distance from the inner end of the insulator and contacts theside wall of the shell to center the insulator in the shell, and annularmeans to hold the insulator in place in the shell seated on the annularmember.

HECTOR RABEZZAN A.

